The contractor shall exert its best efforts to study the enzymatic activity of polycyclic hydrocarbon-metabolizing enzyme systems in human populations as follows: Participate in a blind study to ascertain the reproducibility of the enzyme assay in duplicate or triplicate blood samples from approximately ten individuals per week; Evaluate the reproducibility of the enzyme activities in samples obtained from the same individual at various time intervals; Determine the reproducibility of the enzyme assay in different laboratories by assaying the same blood samples and determine the reproducibility of assays on blood samples taken from the same subject at intervals; Screen patients with bronchial, oral, and skin carcinomas, and control subjects, for enzyme activity at the rate of 40 subjects per week; and Perform genetic studies of enzyme values to be carried with families of the cancer subjects and with suitably matched control families.